1. Field of the Invention
This invention relates to a selectively plating apparatus for forming an annular coated area.
2. Description of the Prior Art
FIG. 1 shows a lead frame. It is only the free ends b of inner leads a and islands c that are plated with gold, silver, etc. A known apparatus for the partial plating of those portions includes a mask member 21 having an opening 21a so sized as to enclose each group of the ends b of inner leads a and the corresponding island c and a mask support 22 having a hole 22a aligned with the opening 21a of the mask 21. The apparatus is shown in FIG. 2. When a lead frame 23 is plated, it is placed on the mask 21 so that the ends b of the inner leads a and the island c may be aligned with the opening 21a. A plating solution is received under pressure from a pump and jetted out through a pressure vessel 27 and a nozzle 24 against the lead frame 23 which is held against the mask member 21 by a pressing plate 26. A sheet of rubber 25 is disposed between the lead frame 23 and the pressing plate 26. The pressure vessel 27 is used for supplying the plating solution uniformly to the area to be plated. An anode is connected to the plating solution, and a cathode to the lead frame, though they are not shown.
If the lead frame is of the type in which an IC element is bonded by an adhesive, however, no plating is required for the island c, but it is sufficient to form an annular coated area around the island c, i.e., only the ends b of the inner leads a which are required for wire bonding. Such a lead frame can be plated by the apparatus of FIG. 2 if the island c on which an IC element is mounted is masked. This, however, presents a great deal of difficulty especially when a large number of lead frames must be plated on a mass production basis. Moreover, it is highly desirable to plate only the ends of the inner leads in order to save gold and silver.